Ultraviolet sterilization and disinfection has been used in various sterilization and disinfection fields. An ultraviolet source may be an ultraviolet LED or an ultraviolet mercury vapor discharge lamp. In the field of air purification, ultraviolet may be used to inactivate harmful substances in the air, so as to improve air quality. Ultraviolet may destroy DNA and RNA of microorganisms, thus killing the microorganisms. Furthermore, ultraviolet may decompose some harmful organics, where the decomposition may be better carried out when combining with oxygenolysis effect of ozone, hydrogen peroxide and the like. Whatever type of the ultraviolet source is, ultraviolet dosage determines the ultraviolet sterilization and disinfection effect, that is, single time microorganism killing rate and single time harmful organics removing rate.
Ultraviolet dosage equals to ultraviolet illuminance multiply irradiation duration. Theoretically, each of the microorganisms like bacteria and viruses within the region that is exposed to ultraviolet irradiation need to be subjected to enough dosage of ultraviolet irradiation in order to be killed. Theoretically, a low ultraviolet dosage may be used to effect sterilization and disinfection, combing with prolonged irradiation duration. Although this method is easy to carry out, it has intrinsic drawbacks. In order to prolong the ultraviolet irradiation duration, it is generally required to increase the area or volume of the region to be sterilized by ultraviolet irradiation so as to effect thorough sterilization and disinfection, which is generally impractical. In ultraviolet sterilization and disinfection, taking into account the volume and cost of the ultraviolet sterilization and disinfection device, generally low ultraviolet illuminance and short irradiation duration are used, and irradiation times are increased through circulated irradiation. This is very low in efficiency.
As to the ultraviolet sterilization and disinfection device within the air pipes of the existing air purifier and central air-conditioner, conventional mercury vapor discharge ultraviolet lamp with power of 4 W (watt), 8 W, 15 W, 20 W, 30 W or 40 W is used. On the one hand, current or power density and thus ultraviolet illuminance are low. On the other hand, no ultraviolet sterilization and disinfection chamber is provided, thus the time that air passes the ultraviolet sterilization and disinfection region is short, and the actual ultraviolet dosage is far less than required. As compensation, the process is performed many times, and filtration is also used. However, single time microorganism killing rate is low, and risk still prevails when it comes to highly infectious and highly pathogenic bacteria and viruses. Take a commercially available small air purifier provided with ultraviolet sterilization and disinfection for example, a small ultraviolet lamp with an outer diameter of 15 mm and power of 4 W is used combined with photocatalyst, the inner face of the sterilization and disinfection chamber is coated with titanium dioxide, and the wind speed is 1.5 m/s. It turns out that, ultraviolet dosage is far less than 1 mJ/cm2, photocatalyst cannot kill the bacteria efficiently, and thus the whole system cannot achieve a good sterilization and disinfection function. Taking hand-push medical sterilization and disinfection cart as another example, the sterilization and disinfection chamber is a cuboid chamber, the length, the width and the height of which are 60 cm, 40 cm and 10 cm, respectively. Three H-shaped ultraviolet lamps are used, disposed in parallel. The ultraviolet lamps have a diameter of 19 mm, an output power of 40 W and a wind speed of 2.0 m/s. The marginal minimum illuminance is 5 mW/cm2, the average ultraviolet dosage is 0.3 mJ/cm2 (mWs/cm2) and the flow rate is 0.48 m3/s. Reference dosage is 5 mJ/cm2 (mWs/cm2), and reference flow rate is 10 m3/h (0.00278 m3/s). In prior art, in order to obtain the reference dosage of 5 mJ/cm2, the ratio of the volume of the ultraviolet sterilization and disinfection chamber to the flow rate (per sec) should be 0.83. And in the case of the reference flow rate of 10 m3/h, in order to obtain the reference dosage of 5 mJ/cm2, it is required that the output power of the ultraviolet lamp should be 23.2 W.
For an existing ultraviolet air disinfection device, the design is simple, ultraviolet dosage is far less than required, single time sterilization and disinfection efficiency is low, and therefore the overall sterilization and disinfection efficiency is undesirable. Also for a conventional ultraviolet lamp, the tube current density is less than 0.2 A/cm3 and ultraviolet illuminance around the lamp is low. In order to achieve the ultraviolet dosage capable of killing microorganisms, it is required to use a large number of ultraviolet lamp and very long ultraviolet sterilization and disinfection chambers. Under this condition, if it is to increase the ultraviolet dosage and single time sterilization and disinfection efficiency, on one hand the device would be bulky and expensive and thus inconvenient to deploy. On the other hand, with heat conduction of gas flow, a conventional ultraviolet lamp with a standard wavelength of 253.7 nm decreases significantly in power efficiency, with significant power loss. The value V/(JQ) which equals to the ratio of the volume V of the sterilization and disinfection chamber to the ultraviolet dosage J and flow rate Q, and the value P/(JQ) which equals to the ratio of the output power P of the ultraviolet lamp to the ultraviolet dosage J and flow rate Q are two of the most important criteria for assessing the properties of an ultraviolet sterilization and disinfection device. In prior art, for a reference dosage of 5 mJ/cm2 and a reference flow rate of 10 m3/h (0.00278 m3/s), in order to obtain the reference dosage of 5 mJ/cm2, the ratio of the volume of the ultraviolet sterilization and disinfection chamber to the flow rate (per sec) should be larger than 0.8, and in the case of the reference flow rate of 10 m3/h, in order to obtain the reference dosage of 5 mJ/cm2, it is required that the output power of the ultraviolet lamp should be larger than 22.0 W.
In public places, fire control facilities are often used to cope with a sudden fire. However, spread of SARS, H7N9 and other emergent and highly infectious and pathogenic microorganisms also greatly threatens public health security. In the case of intensified pollution, those microorganisms may be entrained by and spread by means of particles (PM10, PM2.5 for example) of a haze, which would pose threat to a large number of people. There is an instant need for practical and effective technical solutions and related devices to cope with the problem.